This was a prospective, single-center, and evaluator-blinded study. Twenty-seven Thai patients, both male and female, aged between 30 and 55 years, with a maximum body mass index of 30 kg/m2 and mild to moderate facial laxity (1.5–2.5 points, according to a 4-point Quantitative Grading Scale for laxity) [27] were included. Patients were excluded if they: (1) were pregnant or lactating; (2) had a history of keloid or hypertrophic scar formation, of botulinum toxin, mesotherapy, or laser treatment in the last 6 months, or had a histroy of filler injection in the last 12 months; (3) had concurrent dermatological disease, autoimmune disease or infection in the targeted area; or (4) were currently using medications, including antibiotics, anticoagulants, vitamin C or E supplementation, steroids, or nonsteroidal anti-inflammatory drugs Other exclusion criteria were a history of allergy to p(LA-CL), local anesthesia, or adrenaline; a history of smoking; and signs of non-cooperation or non-compliance with medical treatment requirements.

All patients underwent one session of thread implantation for lower facial laxity using either short (12 cm) or long (23 cm) absorbable barbed threads, which differ based on the lengths of their barbed sections bound by two straight, cut-edge needles of 10 cm, respectively [29] (Definisse™; RELIFE, Menarini Group, Florence, Italy). The absorbable thread presents barbs only within its intermediate areas and is smooth at its ends and midsections [29].

Barbed threads allow the creation of a “J stitch” during implantation to reinforce the device’s anchoring and support capacity. The J stitch is performed by reintroducing the needle into the needle exit hole and rotating it at a 20°–30° angle with respect to the inserted thread. The needle is inserted to a depth of 2 cm and is then removed by pulling it out completely through the skin. Extracting the needle in this way also completely pulls the thread out along with it, allowing it to penetrate the skin. The acute angle between the two tracts of thread and the opposing orientations of the barbs (Fig. 1a) increase considerably the thread’s holding force and resistance to slipping and compresses the tissues between the angles. Generally, when an angle is created with a barbed suture, the holding strength of the thread increases at that specific point [30].

a, b Schematic of the “J stitch” thread implantation using a bidirectional barbed thread with its smooth and barbed parts and needles (a) and the entry and exit points of “J stitch” thread implantation (b)

All patients were treated with the following jawline reshaping procedure. The length of barbed section was selected according to the patient’s facial dimensions. If the distance between the entry and exit points exceeded 7 cm, the 23-cm thread was chosen. The goal of thread placement was to reposition the lower face fat compartments, specifically the inferior jowl fat, middle cheek fat and lateral cheek fat, and to restore jawline definition. Before implantation, the entry and exit points were marked with a line starting at the level of the ear at the infra-auricular region, between the ear lobe and the posterior border of the platysma muscle, posterior to the mandibular angle. One exit point was marked at the medial border of the jowl defect and lateral to the marionette line; a second exit point was marked inferior to the sideburn. The line was extended to the mandible angle and along the jawline toward the midface and then superiorly to a midpoint between the chin and lip, before returning to the starting point (Fig. 1b). The reshaping lines that join the entry and exit points mark the path that the thread would traverse when pulled through the skin.

Preoperatively, 1% lidocaine with adrenaline was injected through the entry and exit points. The entry points were created by inserting an 18G needle perpendicularly into the skin and approximately 5 mm into the subcutaneous tissue, with an exit point created approximately 4–6 cm distant the entry site. The thread was then inserted along the mandibular angle and the tails of the suture along the length of the mandibular ramus before subsequently exiting 4–6 cm distant. To ensure that the barbs of the thread were properly situated within the soft tissue, the device was pulled taut at both the entry and exit points. Post-procedure, fusidic acid ointment was applied to the area twice a day for 1 week. Patients were advised to wash and dry the treated area gently without exerting force, and if applying makeup to the treated area, to do so gently. They were also advised to avoid high-impact sports for 7 days and to avoid dental procedures, visiting saunas, or applying massage and heat to the treated area for at least 1 month.

The primary outcome of the study was a clinical improvement in the grade of lower face and jawline laxity and soft tissue ptosis using a 6-point scale: worse, no lifting effect (no change), mild lifting effect (1–25%), moderate lifting effect (26–50%), marked lifting effect (51–75%), and excellent lifting effect (76–100%). An improvement of 100% indicates the absence of skin laxity while no improvement (0%) indicates no change between pre- and post-treatment states. Photographs were subjectively evaluated by two blinded dermatologists at baseline, immediately after the treatment, and at 1 week and 1, 2, 3, 6, and 12 months follow-up. All clinical photographs were taken with identical camera settings, lighting, and positioning using a Canon PowerShot G9 stand-off camera (OMNIA Imaging System, Canfield Scientific Inc., Fairfield, NJ).

In addition, facial volume in the jawline, nasolabial folds, and submental area were objectively evaluated using three-dimensional photographs captured by the Vectra H1 Imaging System® (Canfield Scientific Inc.). Patients also performed self-assessments using the same 6-point scale as described above at their follow-up visits (1 week and 1, 2, 3, 6 and 12 months after treatment). At every follow-up visit, pain was rated from 1 to 10 using a visual analog scale. Any adverse reactions, including bleeding, edema, bruising, and dimple formation, were also evaluated, as per the study protocol.

Descriptive analysis was used for the demographic data. Volume changes in the facial areas were calculated using the one-sample t-test, and the adjusted p value of < 0.007 was considered statistically significant. Statistical analyses were performed using SPSS Statistics for Windows, version 18.0 (SPSS/IBM Corp., Armonk, NY, USA).

This study was approved by the ethics committee of the Siriraj Institutional Review Board (Certificate of Approval Number: si293/2017). Written informed consent was obtained for the publication and use of all patients’ images prior to their enrollment in the study. This study was performed in accordance with the Helsinki Declaration of 1964 and its subsequent amendments.